One form of scaffolding for receiving materials and providing work platforms for workers at selected vertical levels adjacent to a structure being worked on is a modular structural system that includes load-bearing panels stacked vertically and forming vertical columns, horizontal landing channels at each level that are affixed perpendicular to and supported by the columns, and horizontal joists or "ledgers," which are parallel to the columns, perpendicular to the landing channels, and supported by and affixed to the landing channels. Each load-bearing panel is usually a planar truss that has two tubular posts, which are joined by cross members and diagonal braces. The stacks of load-bearing panels that form the columns are arranged in pairs, each column of each pair being parallel to the building face and one column of each pair being closer to the building face than the other. The pairs of columns are spaced apart laterally, and each column is joined to an adjacent column by cross-bracing trusses that are also parallel to the building face.
The modular scaffolding system thus consists of rectangular bays of two forms. One form of bay, a "load-carrying bay," has two sides parallel to the building face, each of which is a stack of load-bearing panels forming a column, and two sides perpendicular to the building face formed by landing channels. Commonly, each landing channel is "sistered" with a cantilevered extension channel, which has a portion coextensive with the landing channel and a cantilevered portion that extends toward the building from the structural bay and supports a cantilevered deck portion of a width of, say, four feet, for workers to move freely from place to place horizontally along the structure being worked on. The other form of bay, a "cross-truss bay," is located between each adjacent pair of load-carrying bays and usually consists of cross trusses that are co-planar with and joined to the stacks of load-bearing panels that form the columns of the adjacent load-carrying bays. The ledgers span both the load-carrying bays and the cross-truss bays. Decking is attached to the ledgers, which receive wood strips to which the decking is attached by nails.
Each vertical load-carrying bay is essentially a hollow vertical tower that is self-supporting, provided that it is suitably fastened to the building at intervals. Therefore, it is possible for a scaffolding to include adjacent load-carrying towers that are independent of each other, that is, not connected by cross-bracing parallel to the building. It is also possible to construct scaffolding composed of units that consist of two or more load-bearing towers, the adjacent towers of each unit being spaced apart and joined by cross-bracing trusses. Adjacent side-by-side towers or multiple tower units may be relatively widely spaced apart, such that standard ledgers are not strong enough to span the spacing. It is, of course, possible to provide special ledgers that are stronger than the standard ledgers to span greater distances between scaffolding towers. Generally, such special, stronger ledgers may not integrate well with a modular system that uses standard ledgers and other standard parts and increase the cost of the scaffolding.
An exemplary scaffolding system is described and shown in U.S. Pat. No. 5,135,077, issued Aug. 4, 1992, and entitled "Scaffolding System," which is hereby incorporated into the present specification for all purposes.
One object of the present invention is to provide a way of supporting decking across spans between adjacent scaffold towers that are spaced so widely apart as to preclude the use of standard ledgers. Another object is to provide long ledger trusses that use standard ledgers and cross tie bars as major components. Still a further object is to provide long ledger trusses that not only use standard ledgers but do so without modifying them in any way, thus permitting the standard ledgers to be used normally or in a ledger truss. It is also desired to provide ledger trusses that integrate readily into a scaffolding system that uses standard ledgers.